Many means are known for accelerating an object. Relatively small projectiles are efficiently accelerated via controlled explosive charges, such as with gunpowder. As the mass of the object being accelerated increases, however, the explosive force required greatly increases. For example, chemical combustion rockets are presently the only means that have been shown to be effective for launching payloads into space. Although much work has been done in attempting to develop alternative technologies for rapid acceleration of large payloads, such as electromagnetic guns, thermal guns, and plasma arc acceleration, no alternative technology to date has been proven useful and reliable, particularly in the launch of space vehicles.
In relation to space launch, while rocket propulsion is a long proven technology, reliance solely on conventional rocket launch is problematic in that it remains expensive, dangerous, and is dominated by government funding. Such problems are illustrated by the retirement and lack of suitable replacement for the National Aeronautic and Space Administration's Space Shuttle program. The lead time for a new space launch using rocket propulsion is typically three to ten years. Space launches are infrequent, typically occurring less than once a year to a few times per year per customer. This has hampered advancements in certain technologies, such as communications. For example, satellite technologies have been slow and expensive to develop and are often outdated quickly after launch and satellite placement. These factors and attendant continued government involvement have locked in high costs and low profits. In particular, it is widely understood that present rocket launch technology can cost $2,000 to $10,000 or more per kilogram of material for placement in an earth orbit.
Many types of gun launch systems have been proposed as alternatives to rockets. Thermal guns are one previously proposed alternative. Conventional thermal guns have included powder, liquid propellant, and traveling charge thermal guns. Electrothermal guns have included pure electrothermal guns and electrothermal-chemical guns. Light gas thermal guns have included one-stage and two-stage versions. Ram cannon thermal guns have also been proposed. Electromagnetic guns are another previously proposed alternative. Coil versions of electromagnetic guns have included superconducting-type (e.g., quench or DC synchronous), brush-type (e.g., traveling wave, expanding front, and collapsing front), and inductive-type (e.g., single phase and multiphase). Rail versions of electromagnetic guns have included DES-types and breech fed-types (e.g., augmented and simple).
Proposed thermal gun systems share the common feature of being limited by the sound speed of the propelling gas. Thus, for practical engineering reasons, these gun systems are limited to roughly the speed of sound of the propelling gas. Rocket systems are not limited in this manner. Electromagnetic guns are theoretically not limited by the sound of speed of a propelling gas, but experimental results with electromagnetic launchers have indicated that the performance of the launcher does not follow theoretical predictions due to instabilities in the plasma armatures that form above velocities of 2,000 to 4,000 m/s. Above those velocities, the plasma armature instabilities excited by the high magnetic fields in the launchers cause the electrical currents to flow in undesirable places, and energy in the launcher is dissipated rather than being applied effectively to accelerating the projectile. The intractable physics of this phenomenon is similar in some ways to that of magnetic confinement fusion, which is well known to offer many barriers to practical application due to various plasma instabilities in the presence of high magnetic fields
All of the foregoing gun launch approaches, both thermal and electromagnetic, share a common feature in that they impose excessively great acceleration forces on the payload. Accelerations are typically tens of thousands of G's. These accelerations are a fundamental consequence of the physics of operations of gun launch systems attempting to achieve high velocities. The maximum velocity which can be achieved by gun systems is proportional to the square root of the acceleration. Consequently, the acceleration must increase as the square of increasing launch velocity. These accelerations impose enormous challenges in designing payloads that can survive the launch and still accomplish complex tasks after launch. Despite these challenges, perceived payoffs were so high that the US government invested hundreds of millions of dollars in research and development of all the various types of gun launchers in the 1970's through the early 1990's.
A major advantage of rocket propulsion versus gun propulsion is that the ultimate velocity achievable is independent of acceleration rather than being limited to a proportion of the square root of acceleration. However, a major limitation of rocket propulsion is that the mass fraction of the total vehicle mass represented by the payload mass is limited by physics of the well known rocket equation. This physics causes the payload fraction to decline exponentially with the ratio of the ultimate achieved velocity relative to the exhaust velocity of the rocket. Chemical rockets are limited to exhaust velocities of about 2,000 to about 4,800 m/s due to the limitations of chemical reaction energies. Thus, as the total velocity required for the mission increases well beyond 4,800 m/s, the total payload fraction grows small. For reaching Earth orbit, including aerodynamic and gravity losses, the total velocity increment required is about 8,000 m/s. This being substantially higher than available chemical rocket exhaust velocities of 4,800 m/s, the payload fraction is calculated from the rocket equation as being relatively low. Compounding this problem is the parasitic mass of the necessary equipment for the rocket to function, such as, but not limited to, an engine and propellant containers. When these parasitic masses are included, it becomes necessary to limit their effects for launch to Earth orbit by breaking the total velocity into increments, or stages, so that the parasitic mass for each stage can be discarded in order to not hurt the performance of succeeding stages. Historically, two, three, and four stage rocket vehicles have been employed for launching payloads form the Earth's surface to Earth orbit. The total resulting payload fractions to orbit for such vehicles historically have ranged from about 0.5% for smaller rockets, up to about 2.5% for very large rocket systems. This means that the other portion, ranging from 97.5% to 99.5% is either thrown away entirely, or reused to a greater or lessor extent. Recent historical experience with the US space shuttle versus prior and coexistent expendable launchers has indicated that expendable launchers are more cost effective. The expected cost savings of reusability did not materialize for the space shuttle due to the high costs of repairs and refurbishment of the various parts of the space shuttle system due to the very high stresses of launch on its various components.
A few commercial entities have attempted to enter the rocket space launch market; however efficient, cost effective, and reliable launch means are yet to be proven, particularly those suitable for frequent launches. These efforts have been limited by the low payload fractions achievable with chemical rockets, and the necessity of multiple stages that are either expendable or require expensive repairs or refurbishment between launches. The persistently high costs of space launch mean government spending will continue to be an important factor in space launch technologies, and profitability will continue to remain low. Accordingly, there remains a need in the art for systems, methods, and apparatuses for reliable and efficient launch of projectiles, including space vehicles. Desirable characteristics of such systems are low to moderate accelerations, high payload fractions to orbit and escape velocity, and ability to achieve the desired velocity with a single stage rather than multiple stages.